Spoiler reply
I have only a hazy idea of chess strategy, but my understanding is that the way high-level chess works, there are a number of established, recognized strategic positions and moves, and there are general strategies that are widely understood to be the most strategic (like, if you take an expensive piece from your opponent but sacrifice a weaker one of yours to do it, like your rook takes your opponent’s queen but you lose your rook in the process, that’s generally considered a strategic move on your part and a loss on your opponent’s). So because of that, high level players can predict what their opponent is going to do with a certain level of certainty. You generally wouldn’t take your opponent’s knight with your queen if it would mean losing your queen the next turn, for instance. So if that knight is in the queen’s line of fire but is protected by a pawn, it’s probably safe.
But if your opponent decides to throw established strategy out the window, you no longer have certainty. Like if your opponent takes the knight with their queen anyway and basically throws away their most valuable piece for seemingly very little reason, that’s on the surface a really bad move on their part, but it can throw a huge wrench in your plans if you can’t count on your knight to be protected in a scenario like that. So intentionally acting erratic is itself a strategy.
I took it to mean in the context of the murders that Beatrice is prone to excesses that exist just to torment and confuse Battler even though they’re strategically bad moves for her in the context of the game. Like, maybe she sacrifices more people than she needs to (I thought about Natsuhi’s suicide), or she kills them in particularly dramatic ways that leave her more exposed (I thought about her obsession with those locked room mysteries that kept repeatedly happening until it reached a point where it felt truly excessive). I imagine somewhere in all of that, she’s revealed more than she needs to because she just couldn’t help herself. So the question for us then becomes sorting out the stuff she did that was necessary and the stuff that’s actually excessive, which is serving as a distraction.
I dunno, though. That was just how it came across to me.